The overall goal of the proposed research is to extend our knowledge of the specificity and antibody binding characteristics of anti-idiotypic antibodies. Anti-idiotypic antibodies form part of the network that regulates the immune response, by recognizing the idiotype of antibodies and receptors. We plan to study the structure of anti-idiotype antibodies formed against the T15 idiotype in order to dissect this immune response. T15 is the major idiotype observed in the anti-phosphorylcholine response in BALB/c mice. We will work with hybridoma derived anti-idiotype murine antibodies prepared against a monoclonal murine myeloma protein, T15, with anti-phosphorylcholine (PC) activity. To understand the function and relative importance of the anti-idiotypic antibodies and to map out the idiotypic determinant on the T15 molecule, the binding affinity of several antigen binding site specific and near site specific proteins for the T15 molecule will be compared. The anti-antibodies will be further characterized by studying the effects on their binding of the variation of ionic strength, pH, temperature, and the chemical modification of an arginine in the PC binding site of the T15 protein. The binding affinities of the antibody molecules and their Fab fragment will be determined using small zone gel filtration, applying a method developed by us.